U.S. patent application number 10/116129 was filed with the patent office on 2002-10-31 for commanding handover between differing radio access technologies.
Invention is credited to Ovesjo, Fredrik, Van Der Velde, Himke.
Application Number | 20020160785 10/116129 |
Document ID | / |
Family ID | 26813917 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020160785 |
Kind Code |
A1 |
Ovesjo, Fredrik ; et
al. |
October 31, 2002 |
Commanding handover between differing radio access technologies
Abstract
A dual mode mobile terminal (30) is capable of communicating
(e.g., with a core network) either via a first radio access network
(12) having a first type radio access technology (GSM) or a second
radio access network (14) having a second type radio access
technology (UTRAN). When conditions warrant, a network node
prepares a radio access technology (RAT) handover message for
transmission to the equipment unit (UE) in conjunction with
handover of the mobile terminal (MT) from the first radio access
network to the second radio access network, and an associated
change of operation mode of the mobile terminal (MT) from the first
mode to the second mode. In accordance with the present invention,
a radio access technology handover message includes a first
information element representative of a first parameter from which
a value of a second parameter can be derived so that the second
parameter need not be included as a separate information element in
the radio access technology handover message. Not including the
second parameter as a separate element in the radio access
technology handover message facilitates non-segmentation of the
radio access technology handover message. In one aspect of the
invention, the radio access technology handover message is a RRC
Handover to UTRAN message; the first parameter is a Serving-Radio
Network Temporary Identifier (S-RNTI 2); and, the second parameter
is an information element which facilitates distribution of load
and transmission of traffic in the radio access network (e.g., a
Default DPCH Offset Value).
Inventors: |
Ovesjo, Fredrik; (Stockholm,
SE) ; Van Der Velde, Himke; (Zwolle, NL) |
Correspondence
Address: |
NIXON & VANDERHYE P.C.
8th Floor
1100 North Glebe Road
Arlington
VA
22201
US
|
Family ID: |
26813917 |
Appl. No.: |
10/116129 |
Filed: |
April 5, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60282486 |
Apr 10, 2001 |
|
|
|
Current U.S.
Class: |
455/453 ;
455/436; 455/525 |
Current CPC
Class: |
H04W 36/0066
20130101 |
Class at
Publication: |
455/453 ;
455/436; 455/525 |
International
Class: |
H04Q 007/20 |
Claims
What is claimed is:
1. A radio access network which supports radio communication with a
mobile terminal, the radio access network comprising a network node
which prepares a radio access technology (RAT) handover message for
transmission to the mobile terminal, wherein the radio access
technology handover message includes a first information element
representative of a first parameter from which a value of a second
parameter can be derived so that the second information element
need not be included as a separate information element in the radio
access technology handover message.
2. The radio access network of claim 1, wherein the mobile terminal
derives the second parameter from the first parameter.
3. The radio access network of claim 1, wherein the first parameter
is a Serving-Radio Network Temporary Identifier and the second
parameter is a parameter which facilitates distribution of load and
transmission of traffic in the radio access network.
4. The radio access network of claim 3, wherein the second
parameter is a Default DPCH Offset Value.
5. The radio access network of claim 4, wherein the second
parameter (P2) is derived from the first parameter (P1) using an
Expression P2=(P1 mod C)*C2, wherein C1 is a first constant and C2
is a second constant.
6. The radio access network of claim 5, wherein C1 has a value of
one of 599 and 600, and C2 has a value of 512.
7. The radio access network of claim 4, wherein the first parameter
is a parameter to which no further behavior is associated.
8. The radio access network of claim 1, wherein the radio access
technology handover message is a RRC Handover to UTRAN command.
9. The radio access network of claim 1, wherein not including the
second parameter in the radio access technology handover message
facilitates non-segmentation of the radio access technology
handover message.
10. The radio access network of claim 1, wherein the first radio
access network is a Global System for Mobile communications (GSM)
network and the second radio access network is a UMTS Terrestrial
Radio Access network (UTRAN).
11. A telecommunications system comprising: a first radio access
network having a first type radio access network technology; a
second radio access network having a second type radio access
network technology; a mobile terminal having established radio
communication with the first radio access network and which
monitors transmissions from the second radio access network; a
network node which prepares a radio access technology (RAT)
handover message for transmission to the equipment unit (UE), the
radio access technology handover message being transmitted to the
mobile terminal in conjunction with handover of the mobile terminal
from the first radio access network to the second radio access
network; wherein the radio access technology handover message
includes a first information element representative of a first
parameter and from a value of a second parameter can be derived so
that the second information element need not be included as a
separate information element in the radio access technology
handover message.
12. The telecommunications system of claim 11, wherein the mobile
terminal derives the second parameter from the first parameter.
13. The telecommunications system of claim 11, wherein the first
parameter is a Serving-Radio Network Temporary Identifier and the
second parameter is a parameter which facilitates distribution of
load and transmission of traffic in the radio access network.
14. The telecommunications system of claim 13, wherein the second
parameter is a Default DPCH Offset Value.
15. The telecommunications system of claim 14, wherein the second
parameter (P2) is derived from the first parameter (P1) using an
Expression P2=(P1 mod C)*C2, wherein C1 is a first constant and C2
is a second constant.
16. The radio access network of claim 15, wherein C1 has a value of
one of 599 and 600, and C2 has a value of 512.
17. The telecommunications system of claim 14, wherein the first
parameter is a parameter to which no further behavior is
associated.
18. The telecommunications system of claim 11, wherein the radio
access technology handover message is a RRC Handover to UTRAN
command.
19. The telecommunications system of claim 11, wherein not
including the second parameter in the radio access technology
handover message facilitates non-segmentation of the radio access
technology handover message.
20. The telecommunications system of claim 11, wherein the node is
a node of the second radio access network.
21. The telecommunications system of claim 11, wherein the first
radio access network is a Global System for Mobile communications
(GSM) network and the second radio access network is a UMTS
Terrestrial Radio Access network (UTRAN).
22. A method of operating a radio access network comprising
determining when a mobile terminal should be handed over from a
first radio access network having a first type radio access
technology to a second radio access network having a second type
radio access technology; preparing a radio access technology (RAT)
handover message for transmission to the mobile terminal, the radio
access technology handover message being prepared to include a
first information element representative of a first parameter from
which a value of a second parameter can be derived so that the
second parameter need not be included as a separate information
element in the radio access technology handover message.
23. The method of claim 22, further comprising transmitting the
radio access technology handover message to the mobile
terminal.
24. The method of claim 23, further comprising, at the mobile
terminal, deriving the second parameter from the first
parameter.
25. The method of claim 24, wherein the first parameter is a
Serving-Radio Network Temporary Identifier and the second parameter
is a parameter which facilitates distribution of load and
transmission of traffic in the radio access network.
26. The method of claim 22, wherein the second parameter is a
Default DPCH Offset Value.
27. The method of claim 22, wherein the second parameter (P2) is
derived from the first parameter (P1) using an Expression P2=(P1
mod C1)*C2, wherein C1 is a first constant and C2 is a second
constant.
28. The method of claim 27, wherein C1 has a value of one of 599
and 600, and C2 has a value of 512.
29. The method of claim 22, wherein the first parameter is a
parameter to which no further behavior is associated.
30. The method of claim 22, wherein the radio access technology
handover message is a RRC Handover to UTRAN command.
31. The method of claim 22, wherein not including the second
parameter in the radio access technology handover message
facilitates non-segmentation of the radio access technology
handover message.
32. A mobile terminal which is in radio communications with a radio
access network of a telecommunications system, the mobile terminal
comprising: a receiver/transmitter unit which is in established
radio communication with a first radio access network having a
first type radio access network technology and which monitors
transmissions from a second radio access network having a second
type radio access network technology; a network handover function
which processes a radio access technology (RAT) handover message
transmitted to the equipment unit (UE), the radio access technology
handover message being transmitted to the mobile terminal in
conjunction with handover of the mobile terminal from the first
radio access network to the second radio access network, wherein
the network handover function processes the radio access technology
handover message by using a first information element included in
the radio access technology handover message and representative of
a first parameter to derive a value of a second parameter so that
the second parameter need not be included as a separate information
element in the radio access technology handover message.
33. The mobile terminal of claim 32, wherein the first parameter is
a Serving-Radio Network Temporary Identifier and the second
parameter is a parameter which facilitates distribution of load and
transmission of traffic in the radio access network.
34. The mobile terminal of claim 33, wherein the second parameter
is a Default DPCH Offset Value.
35. The mobile terminal of claim 34, wherein the second parameter
(P2) is derived from the first parameter (P1) using an Expression
P2=(P1 mod C1)*C2, wherein C1 is a first constant and C2 is a
second constant.
36. The mobile terminal of claim 35, wherein C1 has a value of one
of 599 and 600, and C2 has a value of 512.
37. The mobile terminal of claim 33, wherein the first parameter is
a parameter to which no further behavior is associated.
38. The mobile terminal of claim 32, wherein the radio access
technology handover message is a RRC Handover to UTRAN command.
39. The mobile terminal of claim 32, wherein not including the
second parameter in the radio access technology handover message
facilitates non-segmentation of the radio access technology
handover message.
40. The mobile terminal of claim 32, wherein the node is a node of
the first radio access network.
41. The mobile terminal of claim 32, wherein the first radio access
network is a Global System for Mobile communications (GSM) network
and the second radio access network is a UMTS Terrestrial Radio
Access network (UTRAN).
42. A method of operating a mobile terminal comprising:
transmitting to measurements pertinent to whether the mobile
terminal should be handed over from a first radio access network of
having a first type radio access technology to a second radio
access network of having a second type radio access technology;
processing a radio access technology (RAT) handover message to
obtain a first information element representative of a first
parameter; deriving from the first parameter a value of a second
parameter pertinent to inter-network handover.
43. The method of claim 42, further comprising, at the mobile
terminal, deriving the second parameter from the first
parameter.
44. The method of claim 43, wherein the first parameter is a
Serving-Radio Network Temporary Identifier and the second parameter
is a parameter which facilitates distribution of load and
transmission of traffic in the radio access network.
45. The method of claim 42, wherein the second parameter is a
Default DPCH Offset Value.
46. The method of claim 42, wherein the second parameter (P2) is
derived from the first parameter (P1) using an Expression P2=(P1
mod C1)*C2, wherein C1 is a first constant and C2 is a second
constant.
47. The method of claim 46, wherein C1 has a value of one of 599
and 600, and C2 has a value of 512.
48. The method of claim 42, wherein the first parameter is a
parameter to which no further behavior is associated.
49. The method of claim 42, wherein the radio access technology
handover message is a RRC Handover to UTRAN command.
50. The method of claim 42, wherein not including the second
parameter in the radio access technology handover message
facilitates non-segmentation of the radio access technology
handover message.
Description
[0001] This application claims the priority and benefit of U.S.
Provisional patent application No. 60/282,486, filed Apr. 10, 2001,
which is incorporated herein by reference in its entirety.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention pertains to wireless
telecommunications, and particularly to inter-radio access
technology handover for wireless telecommunications.
[0004] 2. Related Art and Other Considerations
[0005] Some mobile terminals are capable of using more than one
type of radio access technology (RAT) in order to communicate with,
e.g., other mobile terminals or one or more core networks. Such
mobile terminals have been termed as "dual mode" mobile terminals
in view of their capability to use (e.g., at differing times) at
least two radio access technology types. Each radio access
technology type is implemented using an associated radio access
subsystem or network. Two examples of differing radio access
technologies are (1) the Global System for Mobile communications
(GSM) developed in Europe, and its third generation successor (2)
the Universal Mobile Telecommunications (UMTS) Terrestrial Radio
Access Network (UTRAN). UTRAN is essentially a wideband code
division multiple access (W-CDMA) system.
[0006] An inter-radio access technology (RAT) handover is process
wherein a mobile terminal switches from using a first radio access
system having a first radio access technology (such as GSM) to a
second radio access system having a second radio access technology
(such as UTRA). Inter-RAT handover is normally initiated when the
quality of a downlink radio connection of the first radio access
network falls below a certain level. The quality of the uplink
connection with the first radio access network may be considerably
poorer than the downlink quality.
[0007] In the inter-RAT procedure, a handover command message is
sent to the mobile terminal to provide the mobile terminal with
details of the radio resources to be used after the handover (e.g.,
when the mobile terminal is in communication with the second radio
access network using the second radio access technology). As an
example, consider a situation in which the first radio access
network with which a mobile terminal has been communicating uses
GSM radio access technology (RAT), and wherein measurements warrant
that the dual mode mobile terminal change to use UTRA radio access
technology. In such situation, the handover command message that is
sent by a base station controller of the GSM radio access network
across the GSM air interface to the mobile station comprises one or
more segments of limited length (each segment being twenty one
octets). When a segment of twenty one octets is insufficient to
transmit the radio resource information necessary for the handover,
the handover command message must be segmented to comprise plural
segments. However, after a segment of the handover command message
is sent, a subsequent segment cannot be transferred until receipt
of the preceding segment has been acknowledged.
[0008] The handover command message is sent from the base station
controller to the mobile terminal via the downlink radio
connection. However, in a case in which the handover command
message is segmented, successful transfer of the handover command
message requires that acknowledgement of a preceding segment be
transferred via the uplink radio connection prior to transmission
of a further segment. Thus, if segmentation is used, it may be
impossible to quickly transfer the handover command message due to
poor quality of the uplink radio connection. In other words,
segmentation of the handover command message over more than two GSM
air interface messages can have a significantly detrimental, and
unacceptable, impact on handover performance.
[0009] In the situation of handover from GSM to UTRAN, the GSM
handover command message encompasses a RRC Handover to UTRAN
command message. The RRC Handover to UTRAN command message includes
the details of the UTRA radio resources to be used in the UTRAN
after handover. The RRC Handover to UTRAN command message includes
a large number of parameters stored in respective information
elements of the RRC Handover to UTRAN command message. The size of
the RRC Handover to UTRAN command message depends on the actual
content of these parameters, and can be as long as one hundred to
two hundred octets. When the RRC Handover to UTRAN command message
is so large, it obviously cannot fit within a non-segmented GSM air
interface message, with the result that the RRC Handover to UTRAN
command message must be segmented.
[0010] Various techniques have been utilized as attempts to reduced
the size of the handover command message, and thus to avoid
segmentation of the handover command message. As a first example
technique is preconfiguration. There are two basic types of
preconfiguration. A first type of preconfiguration is pre-defined
configuration. In pre-defined configuration, a network can prepare
and download one or more radio configurations to a mobile terminal.
Such a pre-defined radio configuration comprises a large number of
radio bearer parameters, transport channel parameters, and physical
channel parameters. Prior to RAT handover, the UTRAN inquires which
configurations are stored in the mobile terminal. In case the
mobile terminal has suitable pre-defined configurations stored
thereat, the UTRAN can refer to a stored configuration and then
only needs to signal a few additional parameters to be used in
addition to the stored parameters associated with the pre-defined
configuration.
[0011] A second type of preconfiguration is default parameter
configuration. In default parameter configuration, a number of
parameters are have default values which are specified in a
standard, such as RRC Protocol Specification TS 25.331. The default
parameter configuration can be utilized in a similar manner, but
since it does not need to be downloaded, it can be used more
easily.
[0012] As a second example technique for reducing length of the
handover command message, several initially non-essential
parameters can be omitted from the handover command message. It is
assumed by this technique, however, that the corresponding
functionality of these parameters need not be configured
immediately upon handover.
[0013] As a third example technique, for some of the parameters
transferred when using preconfiguation, the use of smaller value
ranges for the parameters can be predetermined. In other words, the
sizes of certain information elements in the handover command
message is reduced by reserving a subrange of the information
element parameter values for exclusive use by the mobile terminal
which is performing the inter-RAT handover. An explanation of this
third technique is provided in U.S. patent application Ser. No.
09/483,743, filed Jan. 17, 2000, entitled "Method and System For
Improving The Performance of Inter-System Handovers", which is
incorporated herein by reference in its entirety. This third
technique helps to reduce further the size of the handover command
message, although sometimes there is a slight performance
degradation.
[0014] Despite the various techniques that have been used to reduce
the size of handover command messages, the handover command message
nevertheless approaches the limit imposed by the space available in
a non-segmented GSM air interface message. Unless other mechanisms
are defined, hardly any space is left in the RRC Handover to UTRAN
command message to facilitate the inclusion of further
parameters.
[0015] One of the parameters that needs to be included in the RRC
Handover to UTRAN command message, when using preconfiguration, is
a parameter having an information element known as "Default DPCH
Offset Value". Persons skilled in the art will appreciate that DPCH
refers to a dedicated physical channel which corresponds to a
spreading code (see, e.g., 3GPP TS 25.211, v.3.2.0 "Physical
Channels and Mapping of Transport Channels Onto Physical Channels
(FDD)" or 3GPP TS 25.221, v.3.2.0 "Physical Channels and Mapping of
Transport Channels Onto Physical Channels (TDD)"). The Default DPCH
Offset Value parameter is used to distribute evenly the processing
and transmission load of different mobile terminals over time. The
time interval over which the distribution is performed is 80
milliseconds, which corresponds with the maximum transmission time
interval (TTI). Adding the Default DPCH Offset Value parameter to
the RRC Handover to UTRAN command message would introduce an
additional ten bits (600 steps of 512 chips). As indicated before,
this is undesirable since the size of the RRC Handover to UTRAN
command message is already close to the limit for a non-segmented
GSM air interface message.
[0016] What is needed, therefore, and an object of the present
invention, is a technique for facilitating transmission of
additional parameters in a handover command message in conjunction
with inter-RAT handover without appreciably lengthening the
handover command message.
BRIEF SUMMARY
[0017] The present invention pertains to a dual mode mobile
terminal (MT) which is capable of communicating (e.g., with a core
network) either via a first radio access network having a first
type radio access technology or a second radio access network
having a second type radio access technology, as well as to
networks and nodes of such networks which cater to user equipment
units (UE) capable of dual mode operation and to methods of
operating such mobile terminals (MTs), networks, and nodes.
[0018] When the first radio access network is serving the mobile
terminal (MT) in a first mode of operation, the mobile terminal
(MT) monitors transmissions from the second radio access network.
When conditions warrant, a network node prepares a radio access
technology (RAT) handover message for transmission to the equipment
unit (UE) in conjunction with handover of the mobile terminal (MT)
from the first radio access network to the second radio access
network, and in conjunction with an associated change of operation
mode of the mobile terminal (MT) from the first mode to the second
mode. In one example, non-limiting implementation, the first
network (and hence the first mode) is a GSM network and the second
network (and hence the second mode) is a UTRAN network (UMTS
Terrestrial Radio Access Network (UTRAN) of a universal mobile
telecommunications (UMTS) system).
[0019] The radio access technology handover message includes a
first information element representative of a first parameter from
which a value of a second parameter can be derived so that the
second parameter need not be included as a separate information
element in the radio access technology handover message. Not
including the second parameter as a separate element in the radio
access technology handover message facilitates non-segmentation of
the radio access technology handover message.
[0020] In one aspect, the radio access technology handover message
is a RRC Handover to UTRAN message which is transmitted to the
mobile terminal (MT). The mobile terminal (MT) derives the second
parameter from the first parameter. In one example, non-limiting
mode, the first parameter is a Serving-Radio Network Temporary
Identifier (S-RNTI 2) and the second parameter is an information
element which facilitates distribution of load and transmission of
traffic in the radio access network (e.g., a Default DPCH Offset
Value). In one example implementation the second parameter (P2,
e.g., the Default DPCH Offset Value) is derived from the first
parameter (P1, e.g., S-RNTI 2) using the Expression P2=(P1 mod
C1)*C2, wherein C1 is a first constant and C2 is a second constant.
In a specific example for FDD, C1 may have a value such as 599 or
600, for example, while C2 may have a value such as 512, for
example. In a specific example for TDD, C1 may have a value such as
7, for example, while C2 may have a value such as 1, for
example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The foregoing and other objects, features, and advantages of
the invention will be apparent from the following more particular
description of preferred embodiments as illustrated in the
accompanying drawings in which reference characters refer to the
same parts throughout the various views. The drawings are not
necessarily to scale, emphasis instead being placed upon
illustrating the principles of the invention.
[0022] FIG. 1 is a diagrammatic view of a telecommunications system
operating in conjunction with both a first radio access network
having a first type radio access technology and a second radio
access network having a second type radio access technology.
[0023] FIG. 2 is a simplified function block diagram showing
certain example aspects of a representative mobile terminal and
network nodes of FIG. 1 which are involved in an example inter-RAT
handover.
[0024] FIG. 3 is a diagrammatic view of example basic actions
involved in an example inter-RAT handover of a mode of
operation.
[0025] FIG. 4 is a diagrammatic view of a format of an example
handover command message according to a non-limiting
embodiment.
DETAILED DESCRIPTION OF THE DRAWINGS
[0026] In the following description, for purposes of explanation
and not limitation, specific details are set forth such as
particular architectures, interfaces, techniques, etc. in order to
provide a thorough understanding of the present invention. However,
it will be apparent to those skilled in the art that the present
invention may be practiced in other embodiments that depart from
these specific details. In other instances, detailed descriptions
of well-known devices, circuits, and methods are omitted so as not
to obscure the description of the present invention with
unnecessary detail. Moreover, individual function blocks are shown
in some of the figures. Those skilled in the art will appreciate
that the functions may be implemented using individual hardware
circuits, using software functioning in conjunction with a suitably
programmed digital microprocessor or general purpose computer,
using an application specific integrated circuit (ASIC), and/or
using one or more digital signal processors (DSPs).
[0027] FIG. 1 shows a telecommunications system 10 operating in
conjunction with both a first radio access network 12 having a
first type radio access technology and a second radio access
network 14 having a second type radio access technology. In the
non-limiting example shown in FIG. 1, the first radio access
network 12 uses GSM radio access technology, while the second radio
access network 14 uses UTRAN radio access technology. Both first
radio access network 12 and second radio access network 14 are
connected to an external core network 16, such may be (for example)
the Public Switched Telephone Network (PSTN) and/or the Integrated
Services Digital Network (ISDN).
[0028] The core network 16 connects to the first radio access
network 12 (e.g., the GSM radio access network) over an interface
know as the A interface. The first radio access network 12 includes
one or more base station controllers (BSCs) 26.sub.GSM, with each
base station controller (BSC) 26.sub.GSM controlling one or more
base stations (BTSs) 28.sub.G. In the example shown in FIG. 1, base
station controller (BSC) 26.sub.GSM is connected across the Abis
interface to two base stations, particularly base station (BTS)
28.sub.G-1 and base station (BTS) 28.sub.G-2. Each base station
(BTS) 28.sub.G is depicted in FIG. 1 as serving three cells C. Each
cell C is represented by a circle proximate the respective base
station. Thus, it will be appreciated by those skilled in the art
that a base station may serve for communicating across the air
interface for more than one cell, and that differing base stations
may serve differing numbers of cells. The base station controllers
(BSCs) 26.sub.GSM controls radio resources and radio connectivity
within a set of cells, e.g., the cells C.sub.G shown in FIG. 1.
Each base station (BTS) 28.sub.G handles the radio transmission and
reception within one or more cells.
[0029] The core network 16 also connects to the second radio access
network 14 (e.g., the UTRAN radio access network) over an interface
know as the Iu interface. The second radio access network 14
includes one or more radio network controllers (RNCs) 26.sub.U. For
sake of simplicity, the UTRAN 14 of FIG. 1 is shown with only one
RNC node, although typically more than one such node is typically
provided. The RNC node 26.sub.U is connected to a plurality of base
stations (BS) 28.sub.U. For example, and again for sake of
simplicity, two base station nodes--base station (BS) 28.sub.U-1
and base station (BS) 28.sub.U-2--are shown connected to RNC
26.sub.U over an interface known as the Iub Interface. It will
again be appreciated that a different number of base stations can
be served by an RNC, and that RNCs need not serve the same number
of base stations. As in GSM network 12, in UTRAN network 14 for
sake of simplicity each base station 28.sub.U is shown as serving
three cells (each such cell being labeled at least partially as
C.sub.U). In second radio access network (UTRAN network) 14, the
radio network controller (RNC) 26.sub.U controls radio resources
and radio connectivity within a set of cells C.sub.U, while the
base stations (BS) 28.sub.U handle the radio transmission and
reception within one or more cells.
[0030] Each of the aforementioned interfaces, including the A
interface, the Abis interface, a radio interface 32, the Iu
interface, and the Iub interface are shown by dash-dotted lines in
FIG. 1 and FIG. 2.
[0031] A dual mode mobile terminal (MT), such as mobile terminal
(MT) 30, is shown in FIG. 1 as being in radio communication with
first radio access network (GSM network) 12 with an inter-RAT
handover being imminent to second radio access network (UTRAN
network) 14. It will be appreciated that in a GSM context such a
mobile terminal is typically described as a "mobile station", while
in a UTRAN context the mobile terminal is often called a user
equipment unit (UE). As used herein, the term mobile terminal (MT)
generically encompasses both the notion of a mobile station and the
notion of a user equipment unit (UE). The mobile terminal (MT) 30
can be mobile devices such as mobile telephones ("cellular"
telephones) and laptops with mobile termination, and thus can be,
for example, portable, pocket, hand-held, computer-included, or
car-mounted mobile devices which communicate voice and/or data with
radio access network.
[0032] FIG. 2 shows selected general aspects of mobile terminal
(MT) 30 and selected functionalities of nodes such as base station
controller (BSC) 26.sub.GSM and radio network controller (RNC)
26.sub.U. The mobile terminal (MT) 30 shown in FIG. 2 includes a
data processing and control unit 31 for controlling various
operations required by the mobile terminal (MT). The data
processing and control unit 31 of mobile terminal (MT) 30 includes
a mobile terminal inter-RAT handover function 100 and a signal
measurement report function 101, the purposes of which are
described in more detail subsequently. In addition, the data
processing and control unit 31 provides control signals as well as
data to a radio transceiver 33 connected to an antenna 35.
[0033] The example base station (BTS) 28.sub.G shown in FIG. 2
includes a base station data processing and control unit 36.sub.G,
which is connected to one or more base station transceivers (TX/RX)
38. Each base station transceiver (TX/RX) 38 is connected to a
corresponding antenna 39, an appropriate one of which communicates
over air interface 32 with mobile terminal (MT) 30.
[0034] The example base station controller (BSC) 26.sub.GSM shown
in FIG. 2 includes a BSC data processing and control unit 37.sub.G.
Similarly, the example radio network controller (RNC) 26.sub.U
includes an RNC data processing and control unit 37.sub.U. The BSC
data processing and control unit 37.sub.G includes an inter-RAT
handover triggering function 102; the RNC data processing and
control unit 37.sub.U includes a RAT handover command message
preparation function 104. Any or all of mobile terminal inter-RAT
handover function 100; inter-RAT handover triggering function 102;
and RAT handover command message preparation function 104 may be
implemented using individual hardware circuits, using software
functioning in conjunction with a suitably programmed digital
microprocessor or general purpose computer, using an application
specific integrated circuit (ASIC), and/or using one or more
digital signal processors (DSPs)
[0035] As mentioned above, mobile terminal (MT) 30 has a dual mode
functionality, e.g., the capability to communicate with a first
type of radio access technology network such as GSM network 12 and
a second type of radio access technology network such UTRAN network
14. Described herein also are the networks themselves and nodes of
such networks which cater to such dual mode mobile terminals.
[0036] In its various aspects, the present invention concerns one
or more of the preparation, format, transmission, decoding, and use
of a unique and compact handover command message which is utilized
as part of an inter-RAT handover procedure. To illustrate such
aspects, it is assumed in the situation of FIG. 1 that initially
first radio access network (GSM network) 12 is handling radio
communication with mobile terminal (MT) 30. This could mean that,
for example, first radio access network (GSM network) 12 is
currently responsible for paging mobile terminal (MT) 30 regarding
any call (e.g., a call from the core network), or for determining
whether mobile terminal (MT) 30 requests to establish a call (e.g.,
connection). Handling the radio communication with mobile terminal
(MT) 30 can also mean that first radio access network (GSM network)
12 is currently supervising an existing call which involves mobile
terminal (MT) 30. Further, it is assumed that mobile terminal (MT)
30 has the capability to monitor/measure, and does monitor/measure,
the properties (e.g., signal strength) of certain channels
broadcast by second radio access network (UTRAN network) 14.
[0037] FIG. 3 depicts example basic actions involved in an example
inter-RAT handover procedure of a representative mode of the
present invention. Action 3-1 of the inter-RAT handover procedure
of FIG. 3 shows a measurement report message being sent from mobile
terminal (MT) 30 to base station controller (BSC) 26.sub.GSM. The
measurement report message is "enhanced" in the sense that it
includes not only measurements (of, e.g., signal strength) for
selected channel(s) of first radio access network (GSM network) 12,
but also measurements of selected channels for second radio access
network (UTRAN network) 14. The measurement report message is based
upon measurements made and reported by signal measurement report
function 101 of mobile terminal (MT) 30.
[0038] Action 3-2 of the inter-RAT handover procedure of FIG. 3
depicts the inter-RAT handover triggering function 102 of base
station controller (BSC) 26.sub.GSM evaluating the measurements
included in the measurement report message of action 3-1, and
determining whether an inter-RAT handover is necessary. An
inter-RAT handover can be initiated when the quality of the
downlink radio connection with the first radio access network (GSM
network) 12, as reported by the measurement report message of
action 3-1, falls below a predetermined level. In the scenario
shown in FIG. 3, it is assumed that, at action 3-2, the inter-RAT
handover triggering function 102 of base station controller (BSC)
26.sub.GSM determines that an inter-RAT handover is necessary,
e.g., that an inter-RAT handover is desired to handover mobile
terminal (MT) 30 from first radio access network (GSM network) 12
to second radio access network (UTRAN network) 14.
[0039] As a result of the determination of action 3-2 by inter-RAT
handover triggering function 102 that an inter-RAT handover is
desired, as action 3-3 base station controller (BSC) 26.sub.GSM
prepares and transmits a handover required message to core network
16. In response, the core network sends a relocation request
message to the target RNC (t-RNC) as action 3-4. By the relocation
request message of action 3-4, the core network 16 requests the
t-RNC to reserve resources to accommodate the inter-RAT handover.
The actual resource reservation is represented by action 3-5 in
FIG. 3.
[0040] Furthermore, as action 3-6, the RAT handover command message
preparation function 104 of t-RNC prepares an inter-RAT handover
command message. FIG. 4 depicts a non-limiting, example format of
at least selected portions of an example inter-RAT handover command
message generated by the t-RNC as action 3-6. For example, the
example inter-RAT handover command message of FIG. 4 includes a
universal radio network temporary identifier (U-RNTI) information
element 4-1; a serving-radio network temporary identifier (S-RNTI
2) information element 4-2 which is included as part of information
element 4-1; a predefined radio configuration identity information
element 4-3; and physical channel (PhyCH) information elements 4-4.
The predefined radio configuration identity information element 4-3
indicates a predefined configuration of radio base station, traffic
channel, and physical channel parameters to be used. The physical
channel (PhyCH) information elements 4-4 include a scrambling code
number. The particular serving-radio network temporary identifier
utilized in the illustrated embodiment, i.g., S-RNTI 2, is a
special version of the previously-utilized SRNTI that is used in
the inter-RAT handover to UTRAN procedure. A smaller range of
identity values is utilized for S-RNTI 2 in order to reduce the
number of bits in the inter-RAT handover message.
[0041] The radio access technology handover message prepared as
action 3-6 includes a first information element representative of a
first parameter from which a value of a second parameter can be
derived so that the second parameter need not be included as a
separate information element in the inter-radio access technology
handover message. Not including the second parameter as a separate
element in the radio access technology handover message facilitates
non-segmentation of the radio access technology handover
message.
[0042] In particular, in the illustrated scenario in which the
radio access technology handover message is a RRC Handover to UTRAN
message, the second parameter of the RRC Handover to UTRAN command
message is prepared so that the it can be derived by mobile
terminal (MT) 30 from the first parameter of the RRC Handover to
UTRAN command message. As shown in FIG. 4, the first parameter is
the Serving-Radio Network Temporary Identifier (S-RNTI 2) of
information element 4-2, and the second parameter is an information
element which facilitates distribution of load and transmission of
traffic in the radio access network (e.g., a Default DPCH Offset
Value). In one example implementation the second parameter (P2,
e.g., the Default DPCH Offset Value) is derived from the first
parameter (P1, e.g., S-RNTI 2) using the Expression P2=(P1 mod
C1)*C2, wherein C1 is a first constant and C2 is a second constant.
In a specific example for FDD, C1 may have a value such as 599 or
600, for example, while C2 may have a value such as 512, for
example. In a specific example for TDD, C1 may have a value such as
7, for example, while C2 may have a value such as 1, for
example.
[0043] The handover command message as prepared as action 3-6 is
included in a relocation request acknowledgment message sent by
t-RNC to core network 16 as action 3-7. The relocation request
acknowledgment message of action 3-7 thus serves to confirm the
reservation of resources by the t-RNC, and to include the details
of UTRA radio resources to be used after the inter-RAT
handover.
[0044] Upon receiving the relocation request acknowledgment message
of action 3-7, core network 16 next orders performance of the
inter-RAT handover by sending a GSM handover command message to
base station controller (BSC) 26.sub.GSM as action 3-8. The GSM
handover command message includes the details of the UTRA radio
resources to be used after handover, since the GSM handover command
message essentially includes the RRC Handover to UTRAN command
message prepared as action 3-6.
[0045] As action 3-9, the base station controller (BSC) 26.sub.GSM
forwards the GSM handover command message received at action 3-8 to
mobile terminal (MT) 30 over the air interface. Advantageously, in
view of the technique of the present invention, the RRC Handover to
UTRAN command message of the present invention fits within a GSM
handover command message that does not need to be segmented over
the GSM air interface. Thus, action 3-9 includes transmission of
the GSM handover command message over the GSM air interface to 30
over the GSM air interface to 30. The handover command message of
action 3-9 includes the RRC Handover to UTRAN command message
generated as action 3-6.
[0046] Action 3-10 of the inter-RAT handover procedure of FIG. 3
shows the mobile terminal inter-RAT handover function 100 of mobile
terminal (MT) 30 processing the handover command message. Various
sub-actions encompassed in action 3-10 and performed by the mobile
terminal are described in 3GPP TS 25.331 v3.7.0 (2001-06), 3.sup.rd
Generation Partnership Project; Technical Specification Group Radio
Access Network; RRC Protocol Specification (Release 1999), which is
incorporated herein by reference in its entirety. Among such
sub-actions are storing of certain parameters transmitted in the
handover command message of action 3-9; initializing of certain
variables, counters, and timers; and (depending on mode) initiating
radio bearer and transport channel configuration.
[0047] As part of the processing of action 3-10, the mobile
terminal inter-RAT handover function 100 derives or calculates the
Default DPCH Offset Value to be used in the UTRAN by mobile
terminal (MT) 30 from the value of the S-RNTI 2 parameter included
in the handover command message of action 3-9. In the illustrated
example implementation, the Default DPCH Offset Value is calculated
from the S-RNTI 2 using Expression 1 provided above.
[0048] When the radio access network 14 detects the mobile terminal
30, the radio access network 14 knows that the mobile terminal 30
has made the switch or handover from the first network (GSM network
12) to the second network (UTRAN network 14). Accordingly, as
action 3-11 the t-RNC sends a relocation detect message to the core
network 16. This indication may be used to initiate release of the
resources related to the old network.
[0049] Upon successful completion of the inter-RAT handover, as
action 3-12 mobile terminal (MT) 30 also sends a handover to UTRAN
complete message, via the air interface, to the t-RNC. In response,
as action 3-13 the t-RNC sends a relocation complete message to
core network 16. Upon receipt of the relocation complete message of
action 3-13, the core network authorizes release of the GSM radio
connection. Release of the GSM radio connection is realized by a
clear command sent as action 3-14 from core network 16 to base
station controller (BSC) 26.sub.GSM, which is followed by a clear
complete message sent from base station controller (BSC) 26.sub.GSM
to core network 16 as action 3-15.
[0050] Thus, when conditions warrant, a network node of the second
radio access network prepares a radio access technology (RAT)
handover message for transmission to the mobile terminal in
conjunction with handover of the mobile terminal (MT) from the
first radio access network to the second radio access network, and
for an associated change of operation mode of the mobile terminal
(MT) from the first mode to the second mode.
[0051] As described above, in accordance with the present
invention, instead of including the second parameter in the
handover command message, a rule/algorithm is defined for
determining the value of the second parameter (not included as a
separate information element in the handover command message) from
a first parameter which is included in the handover command
message. In the illustrated scenario, the Default DPCH Offset Value
is related to the SRNTI 2 parameter, the SRNTI 2 parameter always
being included in the RRC Handover to UTRAN command message.
[0052] SRNTI 2 is a suitable parameter from which to derive the
non-included second parameter, since the SRNTI 2 parameter is an
information element to which no further behavior is associated.
That is, SRNTI 2 is merely an identity, the value of which can
normally be arbitrarily assigned without having any impact, e.g.,
on behavior of the mobile terminal or system performance or the
like. Thus, the SRNTI is suitable to couple with the second
parameter, e.g., the Default DPCH offset value, and can be
allocated taking the load distribution into account without having
any side effects.
[0053] The solution of the present invention makes it possible from
UTRAN to evenly distribute the loading by assigning SRNTI 2
accordingly, If, however, a minor portion of the load is generated
by the mobile terminals that have been handed over from GSM, UTRAN
may not need to take load distribution into account when assigning
the SRNTI 2 parameter.
[0054] Advantageously, the present invention makes it possible to
distribute the load and transmission for different mobile terminals
without increasing the size of the handover command message message
(e.g., the RRC Handover to UTRAN command message). As a result, it
is possible to transfer the handover command message of the present
invention within a non-segmented GSM air interface. Beneficially,
as a result the performance of the inter-RAT handover is not
compromised.
[0055] The present invention applies both to the UTRA-FDD and the
UTRA-TDD modes of the UTRAN standard as defined by the Third
Generation Partnership Project (3GPP).
[0056] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not to be
limited to the disclosed embodiment, but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
* * * * *